Electrodeposition as a coating application method involves the deposition onto an electrically conductive substrate of a composition under the influence of an applied electrical potential. A coating is deposited as the substrate is immersed in the composition, the substrate serving as an electrode in an electrical circuit of the electrode and a counter-electrode immersed in the composition, the coating being applied to the substrate as electric current is passed between the electrodes.
Often, the composition used in an electrodeposition process includes a resinous phase dispersed in an aqueous medium. While the composition into which the substrate is immersed may include pigments to provide color and other fillers and additives, the properties historically sought by electrodeposited coatings, such as outstanding corrosion resistance, arise primarily because of the deposition of a continuous resinous film. Therefore, the resin content of the composition into which the substrate is immersed is relatively high in relation to the amount of pigment and other fillers. For example, such compositions usually contain 0.02 to 1 parts by weight pigment to 1 part by weight resinous phase.
Lithium ion batteries consist of a cathode, an anode, a separator, and an electrolyte. The cathode is a metal (often aluminum) foil substrate having a lithium-containing active material, such as LiFePO4, deposited thereon. The lithium-containing active material is deposited on the substrate from a slurry containing the lithium-containing active material, conductive carbon, and binder (such as polyvinylidene difluoride) in organic solvent (such as n-methyl-2-pyrrolidone) via a slot die coater or a roll coater. In these slurries, the sum of the amount of lithium-containing active material and conductive carbon is high relative to the amount of binder, typically at least 9 parts by weight to 1 part by weight. The use of such solvent-borne slurries is, however, environmentally undesirable.
As a result, alternative methods and compositions for depositing lithium-containing compositions on a metal foil are desired. The present invention was made in view of the foregoing.